The sound you hear is the motor of the cooling fan that forces air by the control panel and between the oven door glass panels while the oven is hot. It turns on automatically once the oven reaches 120° and stays on until the internal temperature drops below that point. The cooling is completely automatic. There is no reason to adjust. One tip is to leave the oven door open a couple of inched to expedite the cooling off process of the oven. Leaving the oven door closed will increase the cool down time. This is due to the extra insulation that is used to keep the oven hot without using high amounts of energy. The cooling fan is totally separate from the convection fan.